Recent discoveries in the medical field regarding skin cancer and the role of the sun in causing the same have made sunscreens more popular than ever. Moreover, the alarming rate at which the ozone layer was depleted and the slow rate of recovery makes advances in sunscreen technology an important and potentially lifesaving science. Commercially available sunscreens range in potency from two times the skin's naturally occurring UV protection to thirty five and more times the natural state.
Measuring the effectiveness of sunscreens is imperative to rating existing sunscreens with relation to their improvement of the skin's natural abilities and for determining the value of new compositions with regard to the same. The most popular techniques for evaluating sunscreens include in vivo phoyo testing or in vitro transmission methods.
Phototesting involves exposing a portion of a living person's skin to ultraviolet radiation and measuring for a given amount of ultraviolet radiation the time necessary to produce sunburn of a given degree of severity to treated and untreated portions of the subject's skin. More particularly, the amount of time necessary to produce the sunburn without a protective application of sunscreen is noted. The amount of time necessarily increases with the application of sunscreen and the measure of this amount divided by the amount without sunscreen provides the sun protection put on or SPF of the sunscreen.
However, such an approach suffers from a number of problems and limitations. In particular, this method is time consuming. It is also substantially non-reproducible. Naturally, the process is also painful to the subject. As a result of the pain involved, an additional problem includes finding living persons who will willingly submit to such testing. Finally, the evaluation of the degree of the sunburn is a subjective visual evaluation of the irritation.
The other method of evaluation is by in vitro transmission. Solid supports or substrates are coated with the sunscreen, exposed to ultraviolet radiation and a transmission spectrum is taken and compared to similar measurements for non-coated solids or substrates. The problem with this method is that possible reactions by the skin to the sunscreen are not detected.
Equally important to protection, is the evaluation of the ability of the skin to take advantage of the sunscreen's characteristic of improving its ability to protect itself from harmful ultraviolet radiation. That is, while particular sunscreens may provide five times the natural protection to one group of people, it may only provide three times the body's natural protection to another group. In vitro testing is ineffective for this determination.
The current invention solves the problems associated with the above methods of sunscreen evaluation by using live subjects and a machine to measure the effects of ultraviolet radiation with and without sunscreen, and without having to resort to burning.